A recent population-based, household survey of South African men found that nearly 1 in 10 men reported having been sexually assaulted by another man during their lifetime.1 Further examination of this figure uncovers a significant disparity in sexual violence victimization risk: men who report a history of (consensual) sex with men (MSM) are over four times more likely than non-MSM to report male-male sexual violence victimization (34.4% versus 8.1%, p=0.00) as well as perpetration (10.9% versus 2.6%, p=0.00).1 A growing body of public health research and prevention work has emerged to address high rates of sexual violence victimization among South African women, yet the sexual violence risks faced by MSM and other men remain largely unexamined, and the corresponding prevention needs of men have been overwhelmingly neglected. Further, evidence of hypothesized linkages between experiences of male-male sexual violence, sexual risk behaviors, and sexually transmitted infections remains limited in this setting. The study presented here is an initial effort to examine potential risk and protective factors for male- male sexual violence victimization and perpetration among South African MSM. The study holds the following set of specific aims: Aim 1: To determine the 12-month and lifetime prevalence rates of male-male sexual violence victimization and perpetration among a clinic-based sample of 500 MSM; Aim 2: To evaluate a proposed conceptual model of male-male sexual violence victimization, adapted from the Theory of Gender & Power, using structural equation modeling; Aim 3: To evaluate a proposed conceptual model of male-male sexual violence perpetration, adapted from the Confluence Model of Sexual Aggression, using structural equation modeling; and Aim 4: To compare key sexual health behaviors and outcomes, including clinical measures of STI infections, practice of unprotected anal and vaginal sex, and sexual partner concurrency by history of sexual violence victimization and perpetration. To accomplish these aims, the study will recruit a sample of 500 MSM, at least 18 years old, from two public men's sexual health clinics in Cape Town, South Africa. Participants will be asked to complete a computer-administered questionnaire and undergo syphilis and HIV rapid testing. Questionnaire topics include: community norms, relationships, and social life; gender; conflict and violence; sexual behaviors; and alcohol use. Binomial logistic regression and structural equation modeling will be used during data analysis. The study extends the application of a gender-based social theory commonly applied in studies of female rape victimization and builds on the existing psychological model that has predominately been used to study sexual aggression. The study findings will have significant implications for clinical practice, public health theory, and the development of interventions to prevent and mitigate the impact of male-male sexual violence.